Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 180514
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1115 PM CST Wed Jan 17 2018

.UPDATE...
Updated aviation section for 06z taf issuance

Previous update issued at 545 PM CST Wed Jan 17 2018...

The temperature forecast is the main concern for tonight. The
proximity of a surface ridge to our area could potentially keep
surface winds nearly calm for much of the night. Where the snowcover
is deepest and winds are lightest, temps could potentially radiate
much lower than forecast. The area of greatest concern is over
western Kentucky, where southwest flow will be the slowest to
increase aloft. While subzero temps are possible, the forecast has
been updated only to trend them downward in that direction. Will
continue to monitor hourly temps and winds tonight.

&&

.SHORT TERM...(Tonight through Friday night)
Issued at 155 PM CST Wed Jan 17 2018

High pressure will move off to the east, allowing for return
southerly flow, and "warmer" temps through the end of the work
week. For temps we used weighted model output with inputs that
verified best over the past week. That seemed to help account for
snow cover, especially highs. Lows may be a little harder to
gauge. After tonight, winds will stay up overnight and offset the
effects of snow cover. Little if any cloud cover expected until
Friday night.

.LONG TERM...(Saturday through Wednesday)
Issued at 155 PM CST Wed Jan 17 2018

The key synoptic features that are forecast to have an impact on the
moisture return and lift for precipitation late this weekend have
come into the displayable umbrella of the GOES-E (formerly known as
GOES 16) Satellite.

The first feature is the closed low near 47N 138W (basically the
eastern Pacific, off the northwest U.S./southwest Canada coast) at
12z (6am CST) Wednesday. This closed low and the attendant jet
streak rotating in behind it are expected to elongate a trough south
of the low late Thursday into Friday, just prior to the beginning of
the extended forecast period on Saturday. The 00z Wednesday
Canadian, GFS, and ECMWF are amazingly similar with this feature.

The second feature is an evolving low center over southeast Utah at
12z Wednesday.  This feature deepens into a weak low over southern
Texas, before opening up as a wave in Louisiana and the southeast
U.S.  Again, all of the 00z Wednesday medium model runs are similar
with the evolution on this feature as well.

The interplay between these two features will impact the amount of
moisture and lift for the late weekend system.  The Texas low will
effectively cut off the advancing moisture plume from the western
Gulf of Mexico until Friday night/Saturday morning. The timing of
this feature has been quite consistent for the last 48-60 hours of
model runs.

The closed low that deepens the trough axis off the west coast has
been more variable in the range of numerical model solutions,
initially developing a closed low in the four corners of the desert
Southwest, then deepening the low lee of the Rockies, and into the
central Plains. However, the solutions are beginning to converge on
a slightly sharper southwest to northeast trajectory into the
central Plains.  This variability is now the timing, with the 00z
Wednesday Canadian and ECMWF being the slowest with the cold front
approaching the WFO PAH forecast area (6 am CST) next Monday and the
00z Wednesday GFS about 3 to 6 hours earlier.  The latest (12z
Wednesday) GFS is closer to the other guidance.  However, the
overall frontal passage movement into the WFO PAH forecast area has
slowed by 6 to 9 hours.  Although shear will still be significant
during this time period, the front will be moving into the area just
past the diurnal minimum of instability. Depending on the system of
the linear system through the area (progged to be seven hours or
less), this may limit severe and flooding potential (depending on
QPF). The only exception will likely be parts of southeast Missouri
and extreme southwest Kentucky and Illinois, where expected rainfall
amounts will average near 0.75" or higher in less than 12 hours.

Given the slightly slower and more northerly movement of the system
on Sunday into Monday, adjusted Max and Min temperatures upward
approximately one degree from the initialized regionally blended
guidance. The medium range guidance suggest one (and possibly two)
surges of colder air may follow in behind the cold front on Monday,
but temperatures are only expected to fall back to near normal for
this time of year.

The next weather system, showing some similarities to the upcoming
system Sunday into Monday, will likely work across the WFO PAH
forecast area around the 26th or 27th of January.

&&

.AVIATION...
Issued at 1115 PM CST Wed Jan 17 2018

Clear skies will continue through Thursday evening as a surface high
pressure ridge moves east of our area. Light southwest winds will
increase to around 10 kt during the day, then decrease again around
sunset.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

Update...MY
Short Term...CN
Long Term....KES
Aviation...MY



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